1.1. The Problem

In the Distributed Denial-of-Service Open Threat Signaling (DOTS) architecture [RFC8811], DOTS clients and servers communicate using both a signal channel protocol [RFC9132] and a data channel protocol [RFC8783].¶

The DOTS data channel protocol [RFC8783] is used for bulk data exchange between DOTS agents to improve the coordination of parties involved in the response to a Distributed Denial-of-Service (DDoS) attack. Filter management, which is one of the tasks of the DOTS data channel protocol, enables a DOTS client to retrieve the filtering capabilities of a DOTS server and to manage filtering rules. Typically, these filtering rules are used for dropping or rate-limiting unwanted traffic, and permitting accept-listed traffic.¶

The DOTS signal channel protocol [RFC9132] is designed to be resilient under extremely hostile network conditions and provides continued contact between DOTS agents even as DDoS attack traffic saturates the link. The DOTS signal channel can be established between two DOTS agents prior to or during an attack. At any time, the DOTS client may send mitigation requests (as per Section 4.4 of [RFC9132]) to a DOTS server over the active signal channel. While mitigation is active, the DOTS server periodically sends status messages to the DOTS client, including basic mitigation feedback details. In case of a massive DDoS attack that saturates the incoming link(s) to the DOTS client, all traffic from the DOTS server to the DOTS client will likely be dropped. However, the DOTS server may still receive DOTS messages sent from the DOTS client over the signaling channel thanks to the heartbeat requests keeping the channel active (as described in Section 4.7 of [RFC9132]).¶

Unlike the DOTS signal channel protocol, the DOTS data channel protocol is not expected to deal with attack conditions. As such, an issue that might be encountered in some deployments is when filters installed by means of the DOTS data channel protocol may not function as expected during DDoS attacks or, worse, exacerbate an ongoing DDoS attack. In such conditions, the DOTS data channel protocol cannot be used to change these filters, which may complicate DDoS mitigation operations [INTEROP].¶

A typical case is a conflict between filtering rules installed by a DOTS client and the mitigation actions of a DDoS mitigator. Consider, for instance, a DOTS client that configures during 'idle' time (i.e., no mitigation is active) some filtering rules using the DOTS data channel protocol to permit traffic from accept-listed sources. However, during a volumetric DDoS attack, the DDoS mitigator identifies the source addresses/prefixes in the accept-listed filtering rules are attacking the target. For example, an attacker can spoof the IP addresses of accept-listed sources to generate attack traffic, or the attacker can compromise the accept-listed sources and program them to launch a DDoS attack.¶

[RFC9132] is designed so that the DDoS server notifies the above conflict to the DOTS client (that is, the 'conflict-cause' parameter is set to 2 (conflict-with-acceptlist)), but the DOTS client may not be able to withdraw the accept-list rules during the attack period due to the high-volume attack traffic saturating the inbound link to the DOTS client domain. In other words, the DOTS client cannot use the DOTS data channel protocol to withdraw the accept-list filters when a DDoS attack is in progress.¶

1.2. Controlling Filtering Rules Using DOTS Signal Channel

This specification addresses the problems discussed in Section 1.1 by adding a capability for managing filtering rules using the DOTS signal channel protocol, which enables a DOTS client to request the activation (or deactivation) of filtering rules during a DDoS attack. Note that creating these filtering rules is still the responsibility of the DOTS data channel [RFC8783].¶

The DOTS signal channel protocol is designed to enable a DOTS client to contact a DOTS server for help even under severe network congestion conditions. Therefore, extending the DOTS signal channel protocol to manage the filtering rules during an attack will enhance the protection capability offered by DOTS protocols.¶

Conflicts that are induced by filters installed by other DOTS clients of the same domain are not discussed in this specification.¶

An augmentation to the DOTS signal channel YANG module is defined in Section 3.2.2.¶

Sample examples are provided in Section 4, in particular:¶

• Section 4.1 illustrates how the filter control extension is used when conflicts with Access Control Lists (ACLs) are detected and reported by a DOTS server.¶
• Section 4.2 shows how a DOTS client can instruct a DOTS server to safely forward some specific traffic in 'attack' time.¶
• Section 4.3 shows how a DOTS client can react if the DDoS traffic is still being forwarded to the DOTS client domain even if mitigation requests were sent to a DOTS server.¶

The JavaScript Object Notation (JSON) encoding of YANG-modeled data [RFC7951] is used to illustrate the examples.¶

4.1. Conflict Handling

Let's consider a DOTS client that contacts its DOTS server during 'idle' time to install an accept-list allowing for UDP traffic issued from 2001:db8:1234::/48 with a destination port number 443 to be forwarded to 2001:db8:6401::2/127. It does so by sending, for example, a PUT request as shown in Figure 2.¶

PUT /restconf/data/ietf-dots-data-channel:dots-data\
    /dots-client=paL8p4Zqo4SLv64TLPXrxA/acls\
    /acl=an-accept-list HTTP/1.1
Host: example.com
Content-Type: application/yang-data+json

{
  "ietf-dots-data-channel:acls": {
    "acl": [
      {
        "name": "an-accept-list",
        "type": "ipv6-acl-type",
        "activation-type": "activate-when-mitigating",
        "aces": {
          "ace": [
            {
              "name": "test-ace-ipv6-udp",
              "matches": {
                "ipv6": {
                  "destination-ipv6-network": "2001:db8:6401::2/127",
                  "source-ipv6-network": "2001:db8:1234::/48"
                },
                "udp": {
                  "destination-port-range-or-operator": {
                    "operator": "eq",
                    "port": 443
                  }
                }
              },
              "actions": {
                "forwarding": "accept"
              }
            }
          ]
        }
      }
    ]
  }
}

Sometime later, consider that a DDoS attack is detected by the DOTS client on 2001:db8:6401::2/127. Consequently, the DOTS client sends a mitigation request to its DOTS server as shown in Figure 3.¶

Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "mitigate"
Uri-Path: "cuid=paL8p4Zqo4SLv64TLPXrxA"
Uri-Path: "mid=123"
Content-Format: "application/dots+cbor"

{
  "ietf-dots-signal-channel:mitigation-scope": {
    "scope": [
      {
        "target-prefix": [
          "2001:db8:6401::2/127"
        ],
        "target-protocol": [
          17
        ],
        "lifetime": 3600
      }
    ]
  }
}

The DOTS server immediately accepts the request by replying with 2.01 (Created) (Figure 4 depicts the message body of the response).¶

{
  "ietf-dots-signal-channel:mitigation-scope": {
    "scope": [
      {
        "mid": 123,
        "lifetime": 3600
      }
    ]
  }
}

Assuming the DOTS client subscribed to asynchronous notifications, when the DOTS server concludes that some of the attack sources belong to 2001:db8:1234::/48, it sends a notification message with 'status' code set to 1 (attack-mitigation-in-progress) and 'conflict-cause' set to 2 (conflict-with-acceptlist) to the DOTS client to indicate that this mitigation request is in progress, but a conflict is detected.¶

Upon receipt of the notification message from the DOTS server, the DOTS client sends a PUT request to deactivate the "an-accept-list" ACL as shown in Figure 5.¶

The DOTS client can also decide to send a PUT request to deactivate the "an-accept-list" ACL if suspect traffic is received from an accept-listed source (2001:db8:1234::/48). The structure of that PUT is the same as the one shown in Figure 5.¶

Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "mitigate"
Uri-Path: "cuid=paL8p4Zqo4SLv64TLPXrxA"
Uri-Path: "mid=124"
Content-Format: "application/dots+cbor"

{
  "ietf-dots-signal-channel:mitigation-scope": {
    "scope": [
      {
        "target-prefix": [
          "2001:db8:6401::2/127"
        ],
        "target-protocol": [
          17
        ],
        "ietf-dots-signal-control:acl-list": [
          {
            "acl-name": "an-accept-list",
            "activation-type": "deactivate"
          }
        ],
        "lifetime": 3600
      }
    ]
  }
}

Then, the DOTS server deactivates the "an-accept-list" ACL and replies with a 2.04 (Changed) response to the DOTS client to confirm the successful operation. The message body is similar to the one depicted in Figure 4.¶

Once the attack is mitigated, the DOTS client may use the data channel to retrieve its ACLs maintained by the DOTS server. As shown in Figure 6, the activation type is set to 'deactivate' as set by the DOTS signal channel (Figure 5) instead of the type initially set using the DOTS data channel (Figure 2).¶

{
  "ietf-dots-data-channel:acls": {
    "acl": [
      {
        "name": "an-accept-list",
        "type": "ipv6-acl-type",
        "activation-type": "deactivate",
        "pending-lifetime": 10021,
        "aces": {
          "ace": [
            {
              "name": "test-ace-ipv6-udp",
              "matches": {
                "ipv6": {
                  "destination-ipv6-network": "2001:db8:6401::2/127",
                  "source-ipv6-network": "2001:db8:1234::/48"
                },
                "udp": {
                  "destination-port-range-or-operator": {
                    "operator": "eq",
                    "port": 443
                  }
                }
              },
              "actions": {
                "forwarding": "accept"
              }
            }
          ]
        }
      }
    ]
  }
}

4.2. On-Demand Activation of an Accept-List Filter

Let's consider a DOTS client that contacts its DOTS server during 'idle' time to install an accept-list allowing for UDP traffic issued from 2001:db8:1234::/48 to be forwarded to 2001:db8:6401::2/127. It does so by sending, for example, a PUT request shown in Figure 7. The DOTS server installs this filter with a "deactivated" state.¶

PUT /restconf/data/ietf-dots-data-channel:dots-data\
    /dots-client=ioiuLoZqo4SLv64TLPXrxA/acls\
    /acl=my-accept-list HTTP/1.1
Host: example.com
Content-Type: application/yang-data+json

{
  "ietf-dots-data-channel:acls": {
    "acl": [
      {
        "name": "my-accept-list",
        "type": "ipv6-acl-type",
        "activation-type": "deactivate",
        "aces": {
          "ace": [
            {
              "name": "an-ace",
              "matches": {
                "ipv6": {
                  "destination-ipv6-network": "2001:db8:6401::2/127",
                  "source-ipv6-network": "2001:db8:1234::/48",
                  "protocol": 17
                }
              },
              "actions": {
                "forwarding": "accept"
              }
            }
          ]
        }
      }
    ]
  }
}

Sometime later, consider that a UDP DDoS attack is detected by the DOTS client on 2001:db8:6401::2/127 but the DOTS client wants to let the traffic from 2001:db8:1234::/48 be accept-listed to the DOTS client domain. Consequently, the DOTS client sends a mitigation request to its DOTS server as shown in Figure 8.¶

Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "mitigate"
Uri-Path: "cuid=ioiuLoZqo4SLv64TLPXrxA"
Uri-Path: "mid=4879"
Content-Format: "application/dots+cbor"

{
  "ietf-dots-signal-channel:mitigation-scope": {
    "scope": [
      {
        "target-prefix": [
          "2001:db8:6401::2/127"
        ],
        "target-protocol": [
          17
        ],
        "ietf-dots-signal-control:acl-list": [
          {
            "acl-name": "my-accept-list",
            "activation-type": "immediate"
          }
        ],
        "lifetime": 3600
      }
    ]
  }
}

The DOTS server activates the "my-accept-list" ACL and replies with a 2.01 (Created) response to the DOTS client to confirm the successful operation.¶

4.3. DOTS Servers/Mitigators Lacking Capacity

This section describes a scenario in which a DOTS client activates a drop-list or a rate-limit filter during an attack.¶

Consider a DOTS client that contacts its DOTS server during 'idle' time to install an accept-list that rate-limits all (or a part thereof) traffic to be forwarded to 2001:db8:123::/48 as a last resort countermeasure whenever required. Installing the accept-list can be done by sending, for example, the PUT request shown in Figure 9. The DOTS server installs this filter with a "deactivated" state.¶

PUT /restconf/data/ietf-dots-data-channel:dots-data\
    /dots-client=OopPisZqo4SLv64TLPXrxA/acls\
    /acl=my-ratelimit-list HTTP/1.1
Host: example.com
Content-Type: application/yang-data+json

{
  "ietf-dots-data-channel:acls": {
    "acl": [
      {
        "name": "my-ratelimit-list",
        "type": "ipv6-acl-type",
        "activation-type": "deactivate",
        "aces": {
          "ace": [
            {
              "name": "my-ace",
              "matches": {
                "ipv6": {
                  "destination-ipv6-network": "2001:db8:123::/48"
                }
              },
              "actions": {
                "forwarding": "accept",
                "rate-limit": "20000.00"
              }
            }
          ]
        }
      }
    ]
  }
}

Consider now that a DDoS attack is detected by the DOTS client on 2001:db8:123::/48. Consequently, the DOTS client sends a mitigation request to its DOTS server (Figure 10).¶

Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "mitigate"
Uri-Path: "cuid=OopPisZqo4SLv64TLPXrxA"
Uri-Path: "mid=85"
Content-Format: "application/dots+cbor"

{
  "ietf-dots-signal-channel:mitigation-scope": {
    "scope": [
      {
        "target-prefix": [
          "2001:db8:123::/48"
        ],
        "lifetime": 3600
      }
    ]
  }
}

For some reason (e.g., the DOTS server, or the mitigator, is lacking a capability or capacity), the DOTS client is still receiving attack traffic, which saturates available links. To soften the problem, the DOTS client decides to activate the filter that rate-limits the traffic destined to the DOTS client domain. To that aim, the DOTS client sends the mitigation request to its DOTS server shown in Figure 11.¶

Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "mitigate"
Uri-Path: "cuid=OopPisZqo4SLv64TLPXrxA"
Uri-Path: "mid=86"
Content-Format: "application/dots+cbor"

{
  "ietf-dots-signal-channel:mitigation-scope": {
    "scope": [
      {
        "target-prefix": [
          "2001:db8:123::/48"
        ],
        "ietf-dots-signal-control:acl-list": [
          {
            "acl-name": "my-ratelimit-list",
            "activation-type": "immediate"
          }
        ],
        "lifetime": 3600
      }
    ]
  }
}

Then, the DOTS server activates the "my-ratelimit-list" ACL and replies with a 2.04 (Changed) response to the DOTS client to confirm the successful operation.¶

As the attack mitigation evolves, the DOTS client may decide to deactivate the rate-limit policy (e.g., upon receipt of a notification status change from 'attack-exceeded-capability' to 'attack-mitigation-in-progress'). Based on the mitigation status conveyed by the DOTS server, the DOTS client can deactivate the rate-limit action. It does so by sending the request shown in Figure 12.¶

Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "mitigate"
Uri-Path: "cuid=OopPisZqo4SLv64TLPXrxA"
Uri-Path: "mid=87"
Content-Format: "application/dots+cbor"

{
  "ietf-dots-signal-channel:mitigation-scope": {
    "scope": [
      {
        "target-prefix": [
          "2001:db8:123::/48"
        ],
        "ietf-dots-signal-control:acl-list": [
          {
            "acl-name": "my-ratelimit-list",
            "activation-type": "deactivate"
          }
        ],
        "lifetime": 3600
      }
    ]
  }
}

5.1. DOTS Signal Channel CBOR Key Values Subregistry

Per this specification, IANA has registered the following parameters in the "DOTS Signal Channel CBOR Key Values" subregistry within the "Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal Channel" registry [Key-Map].¶

5.2. A New YANG Module

IANA has registered the following URI in the "ns" subregistry within the "IETF XML Registry" [RFC3688]:¶

URI:

urn:ietf:params:xml:ns:yang:ietf-dots-signal-control¶

Registrant Contact:

The IESG.¶

XML:

N/A; the requested URI is an XML namespace.¶

IANA has registered the following YANG module in the "YANG Module Names" subregistry [RFC6020] within the "YANG Parameters" registry.¶

Name:

ietf-dots-signal-control¶

Namespace:

urn:ietf:params:xml:ns:yang:ietf-dots-signal-control¶

Maintained by IANA:

N¶

Prefix:

dots-control¶

Reference:

RFC 9133¶